The present invention relates to a key-phone system, and in particular to a method capable of indicating a communicating duration on a display of a key-phone subset upon a public telephone office line transmission.
In a conventional key-phone system, when a user of a key-phone subset is communicating through a public telephone office line, he or she could not know correctly the calling time of the public telephone office line. Further, in a key-phone system having a particular function, even though it is possible to know the calling time of the public telephone office line, it has only been possible to confirm through a printer connected to the system after the communication. Therefore, in a state during the communication, since a communicator is not able to detect how long the communicating duration of the public telephone office line is elapsed, application of the public telephone office efficiently carried out.